1. Technical Field
The present invention relates to a rheological fluid which is responsive to a magnetic field.
2. Background Art
Rheological fluids responsive to magnetic fields are known. Rheological fluids responsive to electric fields are also known. Such fluids are used in clutches, shock absorbers, and other devices. A characteristic of these rheological fluids is that, when they are exposed to the appropriate energy field, solid particles in the fluid move into alignment and the ability of the fluid to flow is substantially decreased.
Electric field responsive fluids and magnetic field responsive fluids include a vehicle, for instance a dielectric medium, such as mineral oil or silicone oil, and solid particles. In the case of a magnetic field responsive fluid, the solid particles are magnetizable. Examples, of solid particles which have been heretofore proposed for use in a magnetic field responsive fluid are magnetite and carbonyl iron. The fluid also may contain a surfactant to keep the solid particles in suspension in the vehicle.
A brochure published by GAF Corporation of Wayne, New Jersey, containing the code lM-785, captioned "Carbonyl Iron Powders", contains a discussion of carbonyl iron powders marketed by GAF Corporation. The iron particles are classified as "straight powders", "alloys", "reduced powders", and "insulated reduced powders". An example of a "straight powder" which is listed is a powder known as carbonyl "E".
A brief discussion is contained in the brochure concerning magnetic field responsive fluids. It is stated: "The spherically shaped particles of carbonyl iron presumably act like ball bearings in magnetic fluid coupling applications. The smallness of the iron particles gives larger surface area and more contacts than other powders and, hence, better transmission when locked. A lubricant and dispersant are generally required for best results." The discussion contains no disclosure concerning the type of carbonyl iron or dispersant to be employed in a magnetic field responsive fluid.
A publication entitled "Some Properties of Magnetic Fluids", J. D. Coolidge, Jr. and R. W. Halberg, AIEE Transactions, Paper 55-170 (Feb. 1955), pages 149-152, discloses the use of different carbonyl irons in a fluid responsive to a magnetic field. The carbonyl irons disclosed include carbonyl "E" and carbonyl "SF", so-called straight powders, and carbonyl "L", carbonyl "HP"-, and carbonyl "C", all reduced powders. The article contains no conclusions concerning the preference of one carbonyl iron over another in a magnetic field responsive fluid.
A publication entitled "The Magnetic Fluid Clutch" by Jacob Rabinow, NBS Tech. Rep. No. 1213 (1948) [also, Trans. Amer. Inst. Elec. Eng. Preprint 48-238 (1948)] discloses the use of hydrogen reduced iron and carbonyl iron "SF", a "straight" powder as indicated above.
A publication entitled "The Magnetic Fluid Clutch" by S. F. Blunden, The Engineer, 191, 244 (1951) discloses the use of two grades of carbonyl iron, grade "ME" and grade "MC". Grade "ME" is said to be mechanically "hard" and grade "MC" is said to be mechanically "soft". Here also, no preference is given for one carbonyl iron over another.
A publication entitled "Further Development of the NBS Magnetic Fluid Clutch", NBS Tech. News Bull., 34, 168 (1950) discloses the use of carbonyl "E" powder in a magnetic fluid. Other compositional information concerning the fluid is also given.
Prior U.S. Pat. No. 4,604,229 discloses the combination of a hydrocarbon carrier with 4%-10% magnetite, 8%-12% electrically conductive carbon black, and a dispersing agent. Powder magnetite (Fe.sub.3 O.sub.4) is the fully oxidized magnetic oxide of iron, carbonyl iron, or iron-nickel. A similar disclosure is contained in U. S. Pat. No. 4,673,997.
U.S. Pat. No. 3,006,656 discloses a magnetic particle shock absorber using a composition which can contain carbonyl iron, a vehicle such as oil, and graphite. Carbonyl iron and magnetite are described as equivalant materials in the composition. It is not indicated in the patent which carbonyl iron was used.
U.S. Pat. No. 2,519,449 discloses the combination of carbonyl E and solid, powdered graphite in a 50/50 blend. The continuous phase or dielectric medium in the composition is air. The graphite functions as a lubricant.
U.S. Pat. No. 2,661,596 discloses a magnetically-responsive fluid which comprises 100 parts of iron carbonyl powder, 10 parts dielectric oil, and 2 parts dispersant, such as ferrous oleate. The form of carbonyl iron used is not disclosed. U.S. Pat. Nos. 2,663,809 and 2,886,151 disclose the use of carbonyl iron in a fluid coupling. The form of carbonyl iron used is not disclosed.
U.S. Pat. No. 2,772,761 discloses an electromagnetic clutch using a magnetically-responsive fluid comprising an iron powder which is an 80/20 blend of plast-iron and carbonyl "E", and a dispersant comprising 39% graphite, 46% naptha, and 15% alkyl resin, by way of example.
In U.S. Pat. No. 4,737,886, an electroviscous fluid is disclosed. The fluid is responsive to an electric field. Fluids responsive to magnetic fields are also discussed. It is stated in the patent that such magnetic fields require "relatively large electric currents and substantial electrical circuits (for example, large coil windings) to cause the proper response in the fluid".
A publication entitled "Quest, Summer, 1986, pages 53-63, by Jack L. Blumenthal, published by TRW Corporation, discloses the composition and properties of a carbonaceous material comprising fibrous carbon particles manufactured in a carbon disproportion reaction. The carbon fibers of the individual particles are intertwined forming a porous structure. The particles are capable of incorporating and suspending other finely divided powders in fluids.